Speaker
Description
We explore if a late-time cosmic acceleration and a mild variation of fundamental constants can be accommodated within a common scalar-tensor framework. The fundamental constants we focus on are the Newtonian gravitational coupling $G$ and the electron mass $m_e$. The scalar-tensor framework under consideration is a generalized Brans-Dicke theory with an additional matter field. The viability of this framework is explored in the context of well-established late-time cosmic expansion history, namely, a standard $\Lambda$CDM expansion and an extended $\Lambda$CDM expansion (where a rational (Pad\'e-like) deformation is considered). We reconstruct and show that the resulting effective potential of the matter field naturally develops a Higgs-like symmetry-breaking structure with a redshift-dependent mass term, leading to a mild evolution of the vacuum expectation value. This variation leads to an evolution of proton-to-electron mass ratio $\mu$ which is compared with observational bounds derived from quasar absorption spectra. We find that in order to accommodate a reasonably mild variation of $\mu$, the Brans-Dicke scalar field must behave as a chameleon.
